PH‐Switchable Complexation between Double Hydrophilic Heteroarm Star Copolymers and a Cationic Block Polyelectrolyte

Abstract

AbstractDouble hydrophilic heteroarm star copolymers of poly(methacrylic acid) (PMAA) and poly(ethylene oxide) (PEO) were synthesized via atom‐transfer radical polymerization (ATRP) using the “in‐out” method. The synthesis consisted of three steps. Namely, ATRP was applied to the preparation of a star macroinitiator with PEO arms and a cross‐linked core resulting from the polymerization of divinylbenzene (DVB) in the first step, chain extension with tert‐butyl methacrylate (tBMA) under ATRP conditions, and subsequent hydrolysis of the tert‐butyl groups afforded (PEO)n‐PDVB‐(PMAA)n heteroarm star copolymers with a cross‐linked microgel core. This novel type of double hydrophilic heteroarm star copolymer can be considered as unimolecular micelles with hybrid coronas. The star copolymers exhibited pH‐dependent solubility in water, being soluble at high pH and insoluble at low pH, due to the formation of hydrogen‐bonded complexes between the PEO and PMAA arms. A mixed solution of the heteroarm star copolymer and a PEO‐b‐PQDMA diblock copolymer, where PQDMA is poly(2‐(dimethylamino)ethyl methacrylate) fully quaternized with methyl iodide, remained stable in the whole pH range, and exhibited an intriguing pH‐switchable complexation behavior accompanied with structural rearrangement.magnified image